Data visualization is the end artifact, but it involves multiple steps – finding reliable data, getting the data in the right format, cleaning it up (an often underestimated step in the amount of time it takes!) And then finding the story you will eventually visualize. Following is a list useful resources for finding data.
TileMill. GitHub - Social Coding. Weave (Web-based Analysis and Visualization Environment)
Degrafa : Declarative Graphics Framework.